1. Filed of the Invention
This invention relates to a rewinding shaft of a slitting machine, and more particularly to a rewinding shaft of a slitting machine used for cutting or slitting lengthwise a flexible elongated material, especially a sheet metal, into strips having different widths.
2. Brief Description of the Prior Art
In a typical conventional slitting machine, a rolled raw material is fed by a feeder, then slit into strips having a desired width or widths by a cutter at one stage of the process for feeding the material, and then rewound on a rewinding shaft. For rewinding the required number of strips, a corresponding number of rewinding drums are locked to only one rewinding shaft by suitable means such as a key so that the drums are prevented from slipping and thereafter, the strips are fixedly rewound on the rewinding drums.
However, this prior art has the following problems. First, burrs are usually generated on the edge of the slit materials (strips). When the strips with burrs are simultaneously rewound on the same rewinding shaft, each strip is subjected to different tensions because each strip has a different diameter due to difference in thickness of the burrs. Therefore, the strips rewound on the rewinding shaft (i.e., coils of the strips on the rewinding shaft) tend to get loosened. In order to retighten each coil of the strips, the coils of the strips, which were once rewound on the rewinding shaft, are removed from the shaft and retightened using suitable tools. During the process of this retightening operation, the strips (i.e., coils) often get scratched to thereby degrade their quality. Also, the retightening of the strips is a troublesome and hard work. There is known a looping method as one way for preventing the loosening. In this looping method, the strips are pressed hard by pads or the like immediate before the rewinding shaft. When a large driving force is applied to the rewinding shaft, the strips are rewound in their tightened states on the rewinding shaft under the effect of a drawing phenomenon against the braking force exerted by the pads immediately before the rewinding shaft. However, the strips having a reduced diameter due to a difference in thickness of the burrs which are not the same in rewinding length to other strips and tend to hang down immediate before the pads. This hanging amount of each strip is increased in proportion to the increased rewinding length thereof. As a countermeasure, a deep hole extending more than ten meters is formed in the surface of the earth to receive the hanging portions of the strips. Therefore, the installing costs of the slitting machine are increased and a very large installation space is required. In addition, the strips are liable to get scratched under the effect of the drawing phenomenon caused by the pressing of the pads.